Various types of thread supply devices are used with circular knitting machines. Usually, they include a storage drum which is rotatably journalled in a holder. The holder is removably secured to the knitting machine which, typically, is formed with a ring to which a plurality of such holders can be clamped, one for each knitting feed. Yarn is supplied to the respective drums of the yarn supply devices through supply guide means, to be there wrapped or looped about the drum to form a plurality of storage windings thereon. The thread is then pulled off the drum at a speed which may correspond to the wind-up speed and taken off through a take-off guide element, such as a guide eye or the like. Stop-motion devices which sense presence or absence of the thread and its tension, are usually associated with the storage drums to sense the thread being supplied to the drum as well as the thread being taken off. If the tension should fail, or if the thread should break, or if excessive tension should occur, for example because thread being supplied to the drum is not taken off smoothly from the supply yarn package, stop-motion signals are generated by the stop-motion devices to interrupt knitting operation of the machine. The machine will not, of course, stop immediately due to its inertia. The storage winding on the thread supply drums should be sufficient, that is, should have sufficient loops wrapped thereabout to permit the machine to continue to knit during the time taken to reach a full stop.
The thread presence or thread tension sensors associated with positive thread supply devices associated with circular knitting machines are of various types; usually, the thread or yarn sensors and the stop-motion devices are so arranged that they are secured to the holder which also forms the journal or bearing for the storage drum, or that they are part of the housing for the holder or for the storage drum. Other types of thread sensors, particularly the supply thread sensors, have been proposed which are separately secured to the knitting machine, for example on an attachment or on a portion of the carrier ring which is used to also secure the thread supply drums to the knitting machine, or located close to the holder rings or holder arrangement for the yarn packages which supply the thread or yarn to the knitting machine. The trailing or take-off thread sensors are usually secured directly to the holder for the drum, and the necessary electrical switches are retained in the housing thereof.
The thread sensing devices and the associated switches are comparatively delicate. If damage or malfunction occurred on any one of the thread sensors, it was necessary to remove the entire thread supply assembly from the machine for replacement with a properly operating unit and subsequent bench maintenance or repair. This requires not only removal of a thread supply element but, since it is part of the entire knitting machine drive mechanism, comparatively complex disassembly work involving portions of the entire thread supply system for the specific knitting feed. Disassembly work involves disengagement of the thread supply drum from a drive belt which also supplies the other thread supply drums for other knitting feeds; removal of the yarn from the defective thread supply device and rethreading; and resetting and readjusting of the new thread supply drum and the associated thread sensors. There is usually little space for access to the various thread supply drums and the presence of multiple threads adjacent the specific thread supply drum additionally interferes with ready replacement or disassembly.
Some types of yarns are of such characteristics that they are ill suited for cooperation with the normal stop-motion thread sensing devices. Slubbed or other types of yarns which do not present a generally smooth surface are sometimes supplied without passage of the yarn through a stop-motion sensing device associated directly with the yarn supply drum. The presence of stop-motion yarn feelers interferes with smooth pull-off of such threads and, to use the machine with thread or yarn of this type, it is then necessary to disassemble all the thread supply devices and replace them with thread supply apparatus which does not have the stop-motion thread feelers.